1. Field of the Invention
This invention relates to an apparatus and method for recording and processing acoustic signals for use in assessing the condition of the acoustic source. In particular, the method and apparatus is particularly adapted for detecting and recording body sounds, and editing and visually displaying the body sounds for diagnosis and historical tracking.
2. Description of the Related Art
Detecting abnormal sounds is a useful method for diagnosing an abnormal condition in the source of the sound. For example, bearings, engines or other mechanical components often emit abnormal sounds long prior to failure, and detection of such abnormal sounds can be useful in predicting impending failure. While the use of sounds as a diagnostic or assessment method is undoubtedly useful, in practice it is sometimes difficult and limited. Difficulties arise because most sounds of interest occur over a very wide frequency range making detection and analysis difficult. Further, most sounds of interest occur simultaneously with a large number of other, extraneous sounds, making isolation of the acoustic of interest difficult.
Perhaps the most widespread use of monitoring sounds for predicting the condition of the sound source is the use by physicians of the acoustic stethoscope to listen to body sounds. The acoustic stethoscope is a good example of the usefulness and difficulty of using sounds as a diagnostic or assessment method. The acoustic stethoscope has been in use since the early 1800's, and is currently used twice as much as all other diagnostic procedures combined. In addition to widespread use, it has been found that a qualified cardiologist with a stethoscope forms his diagnostic conclusions based on physical examination, auscultation, and patient history, and that this initial conclusion is rarely (less than 6%) altered by secondary testing.
While auscultation is the most widely used method of diagnosis, many problems exist. First, many organ sounds or sounds within organs lie at the edge of human perception due to faint intensity, low or high frequency, high speed, proximity to other sounds, or overall complexity. Second, auscultation is a skill which is difficult to teach, develop, and maintain. Even if a physician can isolate a body sound of interest, a physician must rely solely upon the physician's experience and memory--remembering abnormal sounds is a difficult problem under the best of circumstances. It is not surprising that in testing, a large number of practicing physicians fail basic auscultatory testing using conventional acoustic stethoscopes.
A partial solution to some of the problems associated with conventional acoustic stethoscopes is the electronic stethoscope. U.S. Pat. Nos. 3,160,708 and 3,790,712 (incorporated herein by reference) illustrate such electronic stethoscopes. Electronic stethoscopes in part overcome limitations of the human hearing system by providing a transducer pick-up of the acoustic which is far more sensitive to frequency and amplitude than the human ear. Such electronic stethoscopes also amplify even faint sounds extending the detection range of the human ear.
Notwithstanding their advantages, electronic stethoscopes do not provide a method for recording a patient's body sounds, isolating a particular sound, or displaying the body sounds so that the sound can be heard and also visualized to enhance perception and analysis. It would be a significant advance in the art if a method and apparatus were devised which could electronically detect sound and record, store, edit, and display such sounds for diagnosis and further study. Such accumulation of data would not only aid in assessment and diagnosis, but would also provide an educational medium where auscultatory skills could be improved and maintained and a data base for comparison purposes.